Light Emitting Diodes (LEDs) are widely used for architectural lighting, car headlights and taillights, landscape lights, festival decoration, etc. LED as a light source has such advantages as: power-efficient, orientation-controllable, color-display-stable, long serving life, small size, and very safe to use in various environments, and thus is very fit for scenery lighting or festival decoration. Based on three basic colors, red, green and blue, LEDs can display seven or more colors with a controlling apparatus, which can play an important role in the fantastic display effects of the whole lighting system.
In recent years, with the help of integrated circuit technologies and computer technologies, controlling methodologies based on protocols such as DMX512, DALI, Return-To-Zero have been widely used for LED lighting, and have enabled the computerization and improved the flexibility of LED controlling system.
DMX512 was developed by the Engineering Commission of United States Institute for Theatre Technology (USITT) in 1985. Its physical layer uses RS-485 transceiver, and the bus contains a pair of twisted lines to connect the light modulator and the dimming console. DALI is a lighting control bus solution developed in Europe, an open standard asynchronous serial digital communication protocol.
Now there is in market Return-to-Zero Protocol based technologies, which use one independent controlling signal lines to transfer control signals, by rationing the duty cycles of the red, green and blue LEDs to achieve the controlling over various colors.
Although controlling apparatuses based on the above protocols can achieve various colors from rationing the duty cycles of red, green and blue LEDs, they all need one or more independent signal lines for control signals, and cannot control LEDs by power supply line, thus cannot be applied to the situation where there are only the power supply line and the ground line available.